The invention relates to apparatus for manufacturing power transmission belts, but more particularly, the invention relates to apparatus for molding and curing power transmission belting.
Belting may be processed by apparatus which molds and cures successive incremental portions of belting, or by apparatus which simultaneously molds and cures an entire uncured body into endless belting. This invention is directed to that category of apparatus which simultaneously cures and molds an entire body. Apparatus of this category includes the "shell" and "mandrel" molds. The invention primarily falls within the shell mold category where uncured belting is placed internally of a cylindrical mold member. An expansible member such as a bladder or expansible stock is positioned inwardly of the expansible member. The cylindrical member and expansible member define a mold concavity therebetween. Radially outwardly expansion of the flexible member, with simultaneous application of heat, pressurizes, molds and cures the uncured body. Examples of such apparatus are disclosed in U.S. Pat. Nos. 2,671,244 to Freedlander; 2,573,643 to Hurry; and 2,883,701 to Sauer.
The mandrel curing technique is similar to the shell mold curing technique except that the rigid and flexible portions of the mold are interchanged. The bladder is positioned radially outwardly from the rigid cylindrical member. Uncured belting of individual belt strands or sleeves are interpositioned between the flexible and rigid mold members. The flexible member is displaced radially inwardly under pressure while heat is applied to effect curing and molding of the belting.
The shell and mandrel curing techniques are preferred in the belt making art because they effect molding with a minimum number of irregularities in one inclusive step.
While the shell and mandrel apparatus are accepted standards in the belt making art, their use require cooperation with a sealed heat chamber such as an autoclave. Once placed within an autoclave, special consideration must be given to the mold concavity for proper venting. Shell molds may be vented by means of tiny apertures manifolded together to a vacuum line while the concavity of a mandrel mold may be opened to the autoclave environment or a vacuum line. In either case, special consideration must be given to the molded product to avoid contamination by the autoclave atmosphere. Steam or water may cause blistering of the belting during the curing process.
A problem associated with apparatus that must be placed in an autoclave is interchangeability of the rigid portion of the mold or bladder. The expansible member of the apparatus has limited deformation characteristics and cannot be used with rigid cylindrical members having a circumference change of greater than 20 percent. A bladder of larger diameter must be used.
Another problem associated with prior art apparatus is that of removing the molded belting from the apparatus after completion of curing. Prior art apparatus essentially requires disassembly of component parts of the mold to effect removal. For example, in the apparatus of Freedlander supra, the entire bladder assembly must be removed from the autoclave and the end portions removed before the product can be effectively taken from the mold. The disassembly and reassembly are economical disadvantages. In other words, the prior art does not disclose means for at least partially ejecting molded and cured belting at least partially from the mold so that it can be easily grasped and removed for further processing.
Still another disadvantage with prior art apparatus is that the autoclave in which they are placed requires fluids to be entrapped in the end closures of the autoclave. Such fluid entrapment in the end closures contributes to a heat waste. For example, some belting tensile sections shrink with application of heat. An example of such is a tensile section of polyester cord. During a typical curing cycle, fluids such as steam are directed to all cavities of the mold including the end closures. After a sufficient curing period, the steam is expelled. In a shell type process, the thermal shrinkage associated with a polyester cord tensile section pulls the belting away from the rigid portion of the mold. Fluid under pressure must be maintained within a bladder system while the tensile section cools in an extended condition. Cold water cannot be used immediately with a pressure-heat medium of steam to cool the belting because the steam would immediately condense to water causing a substantial reduction in the bladder pressure. Hot water or other fluid must be used to preclude the bladder from collapsing prematurely. Heat used for voluminous end closures is wasted.